Since these fuels require millions of years to form, for human purposes, the supply of fossil fuels on Earth is effectively fixed. This has led to predictions — such as those based on the "peak oil" theory first proposed by geologist M. King Hubbert in 1956 — that the world will experience an economically damaging scarcity of fossil fuels, particularly oil.

However, new technologies for oil and gas exploration and extraction have upended the notion of fossil fuel scarcity: The limiting factor on humans' fossil fuel use will not be the exhaustion of economically recoverable fossil fuels, but the exhaustion of the Earth's capacity to withstand the harmful byproducts of fossil fuel combustion .